Process of purifying aluminum by distillation of mixtures thereof with other metals



Patented July '4, 1950 Hirsch LoevensteimiNew York, assignor-to Independent Aluminum Corporation, a corporation of York No Drawing. Application September 25, 1946,

' Serial No. 699,336, I

il'Claims. 1

The present invention relates to a process of purifying aluminum by distillation of mixtures thereof with other metals.

It has previously been observed that when a ternary alloy of aluminum, zinc and cadmium is heated under a reduced pressure and ata temperature high enough to distill ofi all of the zinc and cadmium components of the alloy, a substantial part of the aluminum content of the alloy will also be distilled off withthe zinc and cadmium.

- I ture between the meltmg point of the eutectic According to the present invention it is made alloy and the boiling point of aluminum. The temperature will, of course, also depend on the pressure prevailing in the system.

A stream of vapors cfone of the more volatile metals above-mentioned, for example, cadmium, is then passed in contact with the molten bath of aluminum alloy either by bubbling the vapors through the molten aluminum alloy or by caus ing them to sweep over the surface of the bath in contact therewith. The resulting vapor mixture of theconveying metal and the aluminum vapors is conducted to a condenser and condensed. Condensers of various known forms may be-used, If the condenser is of a type and so 1 operated that the condensed metals are recovered brought about by utilizing the ability of certain a relatively volatile metals to entrain aluminum vapors when passed as vapors over or through a molten bath of aluminum or an, aluminum; alloy With one of the higher boiling point metals such as iron, silicon and titanium and thereafter sep-, arating the aluminum so removed from the entraining metal vapors by condensation. 1

The relatively volatile metals selected are those that are either insoluble or only slightly. soluble in liquid aluminum and generally do not mix with aluminum. The metals thatgI prefer to use for this purpose are cadmium, sodium and potassium, although rubidium, caesium and mercury, as well as alloys of two or more of these metals, may be employed. Aluminum may be in the same vessel, they lend themselves to ready separation because of the differences in their specific gravities. After separation, the conveying metal (cadmium, in the example) maybe re-vaporized and returned to the aluminum entraining chamber. I

Alternatively, the mixture of vapors may be passed through a condenser wherein the largerpart of the aluminum vapors are condensed in one chamber and the remaining portion with more or less of the entraining metal is condensed in a second or. successive chambers. Any, portion of the vapors of the entraining metal not condensed is returned for reuse in the cycle. The aluminum from the condenser can be continuously or intermittently removed and, if necessary,- subjected to a second distillation under normal or reduced pressure or a substantial vacuum in order to remove any small quantitles of the conveying metal which may have recovered from vapor mixtures of these metals and aluminum by condensing the vapor mixture and allowing the aluminum to separate from the conveying metal by gravity. The condensed conveying metal may then be returned. to the alumimum-containing bath that is undergoing the separation treatment.

The invention has for an object to obtain aluminum in a high state of purity from alumie mum-containing alloys or impure aluminum as By way of specific example, an aluminum alloy, 3

such as silico-aluminum or ferro-aluminum, as produced in the electric furnace and whichis usually contaminated, respectively, with iron or silicon and also with titanium, is placed in a suitable closed container and hea'tedrto atempera'e remainedad'mixed with the aluminum. By this process a very purealuminum is obtained.

If desired the condensed liquid metal can be directly returned to the aluminum vaporizing chamber and there evaporated instead of distilling vapors thereof in a separate chamber and then transferring these to the aluminum vaporizing chamber.

It is preferable to carry on the operation at a reduced pressure or under vacuum because the vapor pressure of aluminum increases faster with lowering of the pressure imposed on the system than the vapor pressures of the metals alloyed therewith' For example, the boiling points of aluminum, silicon and copper at 760 mm. Hg are, respectively, 2270 C., 2355 C., 2335 C. At a pressure of 1 mm. of mercury these boiling points are: Aluminum, 1030" C.; silicon, 1687 C.; and copper, 1400 C.

.; other advantages obtained by carrying out the,

3 process at a reduced pressure are: a saving of fuel or energy for heating and thepossibility of using metallic containers formed of relatively inexpensive materials such as iron and iron alloys in which tocarry out the treatment.

It will be understood that the process is appli- Y cable in the recovery of aluminum from its com.-.

mercial alloys as well as in purifym raw. alumie num or thermically produced aluminum alloys Various modifications may be made in the,

details of the procedure involved without departing from the invention which is not to be deemed as limited otherwise than as indicated by the appended claims.

I claim:

1. The process of separating aluminum from its alloys with higher boiling point metals having a. relatively lessened tendency as compared to aluminum to vaporize on heating at, reduced pressures such as iron, silicon and titanium, which comprises heating the alloy under reduced pressure in the presence of vapors of a relatively volatile metal selected from the group consisting of sodium, potassium, rubidium, caesium, cadmium and mercury, and, while maintaining the alloy in at least a partly liquid state and below the boiling point of; aluminum at the pressure imposed, withdrawing the resul-tingvapor mixture of aluminum and said selected metal from the heating zone, and thereafter condensing the aluminum vapors and separating the condensed aluminum from said relatively volatile metal.

2. The process of separating aluminum from its alloys with higher boiling point metals having a relatively lessened tendency as compared to aluminum to vaporize on heating at reduced pressures such as iron, silicon and titanium, which comprises forming a molten bath of the alloy and, while adjusting the temperature and pressure thereof Soas to minimize the vapor pressures of the higher boiling point metals present and at the same time vaporizing aluminum from said bath, entraining aluminum vapors evolved from said bath in a current of vapors of a relatively volatile metal selected from the group consisting of sodium, potassium, rubidium, caesium, cadmium and mercury, and thereafter separating the aluminum from said volatile metal by'condensae ticn of the aluminum vapors.

3. The process of separating aluminum from its alloys with higher boiling point metals havinga relatively lessened tendency as compared to aluminum to vaporize on heating at reduced pressures such as iron, silicon and titanium, which comprises forming a molten bath of the alloy-and, while maintaining a substantially reduced pressure and controlling the temperature within av range insuring vaporization of" aluminum from said bath but below a temperature at which the higher boiling point metals present will exhibit substantial vapor pressures, entraini-ng aluminum vapors evolved from said bath in a current of vapors of a relatively volatile metal selected from the group consisting of sodium, potassium, rubidium, caesium, cadmium and mercury, and thereafter separating the aluminum from said volatile metal.

' 4; The process of-separating aluminum-from its alloys with higher boiling point metals having a relatively lessened tendency as compared to aluminum to vaporize on heating at reduced pressures such as iron, silicon and titanium, which comprises forming a molten bath of thealloy. and, a while maintaining a substantially reduced pressure and controlling the temperature within a 4 I range insuring vaporization of aluminum from said bath but below a temperature at which the higher boiling point metals present will exhibit sub sta-ntial vapor pressures, entraining aluminum vapors. evolved irom said bath in a current of vapors of a relatively volatile metal selected from the group consisting of sodium, potassium, rubid- 'entraining additional aluminum vapors and removing them from the region of said bath.

5. Ifhe process of separating aluminum from its alloys with higher boiling point metals having a relatively lessened tendency as compared to aluminum to vaporize on heating at reduced pressures such as iron, silicon and titanium, which comprises forming a molten bath of the alloy and, while adjusting the: temperature and pressure thereof so as to minimize the vapor pressures of the higher boiling point metals present and at the same time vaporizing aluminum from said bath, cut-raining aluminum vapors evolved from said bath in a current of vapors of a relatively volatile metal selected from the group consisting of sodium, potassium, rubidium, caesium, cadmium and mercury, thereafter condensing the vapor mixture and subjecting the resulting condensed mixture to gravity separation, and finally subjecting thealuminum to controlled re-distillation to remove minor amounts of the more volatile metal remaining therein.

6. The process of separating aluminum from its alloys with higher boiling point metals having a relatively-lessened tendency as compared to alu-, minum to vaporize on heating at reduced pres+ sures'such as iron, silicon and titanium, which comprises forming a molten bath of the alloy and, while adjusting the temperature and pressure thereof so as to minimize the vapor pressures of the higher boiling point metals present and at the same time vaporizing aluminum from said bath,

entraining aluminum vapors evolved from said bathin a-current ofsodiu-m vapors, and thereafter condensing the mixture of sodium and aluminum vapors and separating the condensed. aluminum from the sodium by gravity separation.

7. The process of separating aluminum from its alloys with higher boiling point metals having a relatively'lessened tendency as. compared to alu-. minum to vaporize on heating at reduced pres-v sures such as iron, silicon and titanium, which comprises forming a molten bath of the alloy and, while adjusting the temperature and pressure thereof seas to minimize the vapor pressures of the higher boilingpoint metals present and at the sametime vaporizing aluminum from said bath, entraining aluminum vapors evolved from said bath in a current of cadmium vapors, and thereafter condensing the mixture. of cadmium and aluminum vapor-s, separating the bulk of the cadmium from thealuminumby gravity separation, and thereafter subjecting thealuminu-m to re-distillation to drive off the residue of the cadmium.

8. The process of separating aluminum from its alloys with higher boiling point metals having a relatively lessened tendency as compared to aluminum to vaporize on heating at reduced pressures such as iron, silicon and titanium, which comprises-forming a molten bath of the alloy and, while adjusting the. temperature and pressure thereof so as to minimize thevapor pressures 0i":

the higher boiling point metals present and. at the same time vaporizing aluminum from said bath, entraining aluminum vapors evolved from said bath in a current of potassium vapors, and thereafter condensing the mixture of potassium and aluminum vapors and separating the condensed aluminum from the potassium by gravity separation.

9. The process of separating aluminum from its alloys with higher boiling point metals having a relatively lessened tendency as compared to aluminum to vaporize on heating at reduced pressures, which comprises heating the alloy to a. temperature between the melting point of the alloy and the boiling point of aluminum at the 1 pressure maintained, adjusting the pressure to minimize the vapor pressures of said higher boiling point metals present in the alloy, passing a stream of vapor of a relatively volatile metal selected from the group consisting of sodium, potassium, rubidium, caesium, cadmium and mercury in contact with the molten aluminum to form composite vapors of aluminum and the selected relatively volatile metal and separating the aluminum from the said relatively volatile metal.

I-lIRSCI-I LOEVENSTEIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,872,611 Thurm Aug. 16, 1932 1,931,144 Gilbert Oct. 17, 1933 1,961,135 Crahan et a1 June 5, 1934 1,964,593 Nerad June 26, 1934 2,262,164 Brown Nov. 11, 1941 FOREIGN PATENTS Number Country Date 543,468 Great Britain Feb. 26, 1942 

1. THE PROCESS OF SEPARATING ALUMINUM FROM ITS ALLOYS WITH HIGHER BOILING POINT METALS HAVING A RELATIVELY LESSENED TENDENCY AS COMPARED TO ALUMINUM TO VAPORIZE ON HEATING AT REDUCED PRESSURES SUCH AS IRON, SILICON AND TITANIUM, WHICH COMPRISES HEATING THE ALLOY UNDER REDUCED PRESSURE IN THE PRESENCE OF VAPORS OF A RELATIVELY VOLATILE METAL SELECTED FROM THE GROUP CONSISTING OF SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, CADMIUM AND MERCURY AND WHILE MAINTAINING THE ALLOY IN AT LEAST A PARTLY LIQUID STATE AND BELOW THE BOILING POINT OF ALUMINUM AT THE PRESSURE IMPOSED, WITHDRAWING THE RESULTING VAPOR MIXTURE OF ALUMINUM AND SAID SELECTED METAL FROM THE HEATING ZONE, AND THEREAFTER CONDENSING THE ALUMINUM VAPORS AND SEPARATING THE CONDENSED ALUMINUM FROM SAID RELATIVELY VOLATILE METAL. 